This invention relates generally to the field of disc drive data storage devices. More specifically, the invention relates to an improved seal based on condensation phenomenon for use with a disc drive spindle motor to reduce or prevent outgassing from the spindle motor.
Disc drive data storage devices are well known in the industry. Such devices use rigid discs coated with a magnetizable medium for storage of digital information on a plurality of circular concentric data tracks. The information is written to and read from the discs using a transducing head mounted on an actuator mechanism which moves the head from track to track across a surface of the disc under the control of electronic circuitry. The disc or discs are mounted for rotation on a spindle motor which causes the disc to spin at a very high, constant speed and the surfaces of the discs to pass under the heads.
As magnetic storage densities have increased, magnetic disc drives have been required to operate with increasingly greater precision. This requirement has meant that magnetic recording heads have been placed increasingly close to the surface of the magnetic disc. The interaction between the magnetic head and the recording surface has also become increasingly precise. This requires the environment of the magnetic disc to be free from particulate and liquid contaminants which could interfere with this interface between the magnetic head and the recording surface. Typically, the disc environment is sealed during manufacture so that contaminants cannot enter the housing and contact the storage disc or the magnetic recording head. Additionally, it is important that the disc environment within the housing remain contaminant free following manufacturing and throughout the life of the disc drive system. Even micro minute contaminants can have serious results on disc operation. For example, particulate build-up between the transducing head and the disc can cause degradation in the readback signal, head crashes, and damage to the disc surface.
One source of particulate and liquid contaminants in the sealed chassis is the disc drive spindle motor which is located within the housing and supports and rotates the storage disc. The disc rotates at speeds in excess of several thousands of rpm, and the rotational speed in present day disc drives continues to increase. Although efforts are made to seal the motor, the seal is not perfect and especially at high rotational speed, contaminants tend to be generated and escape from the motor into the compartment containing the disc.
In such disc drive spindle motors, it is well known that the liquid or gas in a hydrodynamic bearing or the lubricants in a ball bearing when operated under high speed, high temperature conditions may result in outgassing. Volatile components from the spindle bearing lubricants come out, and come in contact with the relatively cooler disc surface. This phenomenon creates micro droplets, causing HDI failure. With the increasing trend to higher spindle motor speeds, the existence of this phenomenon has made it more challenging to design durable disc drives.
The outgas depends on many factors, including the opening of the meniscus or menisci in the hydrodynamic bearing, the opening of the ball bearing seal or shield, as well as the operating temperature, and the properties of the lubricant (liquid or gas) which support rotation of the bearing.
Several methods have been applied in the prior art to reduce outgassing. One common method is by incorporating a fertofluidic seal. A ferrofluidic seal is efficient at reducing the outgassing, but it brings a new problem by degrading and outgassing itself, especially at high rpm and temperature. The seal is also very expensive. An example of such a ferrofluid seal i s found in U.S. Pat. No. 5,011,165. As shown in this patent, the ferrofluid seal is a fluidic seal, the fluid being held in place by a magnet. The fluid extends across a gap between a fixed portion of the disc drive motor and a rotating portion of the motor, and thereby prevents contaminants from the motor from entering the sealed disc environment defined by the housing. However, as discussed above, the ferrofluid itself may leak from the seal or may outgas and enter the disc environment. Further, especially under high temperature and high rotational speed conditions, the ferrofluid seal may leak into the motor causing damage. Additionally, any leakage of the ferrofluid or other loss of the quantity or quality of the fluid over time reduces the effective quantity of the ferrofluid defining the seal, thereby reducing the effectiveness of the seal.
Another type of seal is a labyrinth seal. Typically, a labyrinth seal is defined by a small gap between a rotating portion and a stationary portion of the motor, the small gap extending over a long path between these two relatively rotating parts. The length and complexity of the path tends to inhibit contaminants from the motor from escaping through the labyrinth into the sealed disc compartment. The effectiveness of the labyrinth seal is dependent on minimization of the gap, and lengthening the path, and maintaining the complexity of the path. However, this requires precision machining which is difficult, time consuming and expensive. Although such seals tend to be less expensive than ferrofluid seals, they are also not as effective in isolating the motor from the disc environment.
Thus there is a continuing need for improving the isolation between the spindle motor and disc drive and the contaminant free disc housing.
The disc drive of the present invention includes a disc drive spindle motor and a chassis or housing for providing a substantially contaminant free cavity for housing one or more discs supported on the spindle motor. The disc drive spindle motor includes a fixed member coupled to the chassis, and a rotor rotatable about the fixed member for rotating a magnetic storage disc in the contaminant free cavity. A bearing, which may be a hydrodynamic bearing, ball bearing or other bearing type, interconnects the fixed member and the rotor, and supports the rotor for rotation relative to the fixed member. According to the present invention, a very simple seal termed herein a condensation seal is supported from either the fixed member or the rotor, adjacent the bearing opening where outgassing may occur. The seal is called a condensation seal as the condensing phenomena will be applied to reduce the outgassing.
The seal incorporates a cooling surface which is supported from either the hub/rotor or the fixed member adjacent the region where outgassing occurs; the surface preferably should be wavy, or fin shaped to provide a maximum surface area for better heat transfer and better cooling effect, so that the surface is relatively cooler than the surrounding operating environment. The surface is shaped and made of a material, e.g. aluminum, and of a thickness to optimize the heat transfer characteristics, so that the hot volatile products of the outgassing phenomenon will condense when they come in contact with the condensation seal surface. The condensation seal surface must have a specified clearance with the fixed member or rotor to avoid any possibility of contact, while maximizing the condensation efficiency by placing the cooling surface directly in the path of the outgassing phenomenon.
It is important to note that the cooling surface must not touch the lubricant of the bearing.
The principles of the invention, as will be described more fully below, can be applied to hydrodynamic bearings of either the thrust plate or conical or spherical, or combination design, or to ball bearings.
Other features and advantages of the present invention will become apparent to a person of skill in this art who studies the description given below of one or more alternative preferred embodiments of the present invention, given in association with the following drawings.